Torque Responses in Human Quadriceps to Burst-Modulated Alternating Current at 3 Carrier Frequencies

Jessica Evenson, Laura Keller, Michael G. Parker

DOI: 10.2519/jospt.2005.1779

Study Design: Independent group design, 1 group per carrier frequency, with subjects stratified by gender and systematically assigned to groups. Objective: To determine the effect of the frequency of burst-modulated alternating current (AC) on the electrically induced torque (EIT) response of the quadriceps femoris muscle. Background: Many studies have examined the influence of current amplitude and burst modulation on the EIT response. However, research is limited on the effects of carrier frequency on the EIT response of the quadriceps femoris. Methods and Measures: Twenty-three healthy subjects (mean age ± SD, 22.7 ± 1.7 years) volunteered for the study and were systematically assigned to 1 of 3 groups: group 1 (2500-Hz AC), group 2 (3750-Hz AC), and group 3 (5000-Hz AC). For normalization purposes, maximal voluntary isometric contraction (MVIC) force was assessed with a load cell prior to the application of 5 minutes of neuromuscular electrical stimulation (NMES). The EIT and current amplitude were recorded during each of the 5 minutes of NMES. Results: The mean EIT ([EIT/MVIC] × 100) produced at equivalent current amplitudes when using the 2500-Hz carrier frequency was significantly greater than the mean EITs generated at 3750 Hz (P = .004) and 5000 Hz (P<.001), respectively. Conclusions: Burst-modulated alternating current delivered at 2500 Hz produced greater EITs than those generated at 3750 and 5000 Hz. J Orthop Sports Phys Ther. 2005;35(4):239-245. Key Words: current amplitude, electrical muscle stimulation, muscle training intensity

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